SY8291FABC

Application Note: SY8291F High Efficiency, 300kHz, 36V Input, 1.2A Asynchronous Step Down Regulator Features The SY8291F is a high efficiency 300kHz, adaptive constant OFF time controlled asynchronous step-down DC/DC regulator capable of delivering 1.2A output current respectively. The SY8291F can operate over a wide input voltage range from 9V to 36V and integrates the main switch with very low RDS(ON) to minimize the conduction loss. Low output voltage ripple and small external inductor and capacitor sizes are achieved with 300kHz switching frequency.  9-36V Input Voltage Range  Low RDS(ON) for Internal N-channel Power FET: 180 mΩ  300kHz Switching Frequency  Adaptive Constant OFF Time Control  Internal Soft-start Limits the Inrush Current  2% 0.81V Reference  RoHS Compliant and Halogen Free  Compact Package: SOT23-6 or 科 立 创 General Description      SY8291 □(□□)□ Typical Applications IN CIN 2.2µF CBS 100nF BS on fi VIN lP Note -- de nti a Package type SOT23-6 Set Top Box Portable TV Access Point Router DSL Modem LCD TV rep are Temperature Code Package Code Optional Spec Code Ordering Number SY8291FABC dF Applications Ordering Information L 10µH VOUT=5V .C LX yC orp D CFF opt. COUT 22µF FB EN R2 20kΩ GND Sil erg OFF/ON R1 105kΩ AN_SY8291F Rev. 0.9 © 2019 Silergy Corp. Figure1. Schematic Diagram Silergy Corp. Confidential- Prepared for Customer Use Only 1 All Rights Reserved. AN_SY8291F Pinout (top view) BS 1 6 LX GND 2 5 IN FB 3 4 EN 立 创 (SOT23-6) Top Mark: qRxyz (Device code: qR, x=year code, y=week code, z= lot number code) GND FB 2 3 EN 4 IN 5 LX 6 Pin Description Boot-strap pin. Supply high side gate driver. Decouple this pin to the LX pin with a 0.1μF ceramic capacitor. Ground pin. Output feedback pin. Connect this pin to the center point of the output resistor divider (as shown in Figure 1) to program the output voltage: VOUT=0.81×(1+R1/R2) Enable control. Pull high or leave this pin floating to turn on the IC, pull low to turn off the IC. Input pin. Decouple this pin to the GND pin with at least a 2.2μF ceramic capacitor. Inductor pin. Connect this pin to the switching node of the inductor. or 科 Pin Number 1 de nti a lP rep are dF Pin Name BS Absolute Maximum Ratings (Note 1) erg yC orp .C on fi Supply Input Voltage ------------------------------------------------------------------------------------------------ -0.3V to 40V EN Voltage--------------------------------------------------------------------------------------------------- -0.3V to VIN+0.6V FB, BS-LX Voltage-------------------------------------------------------------------------------------------------- -0.3V to 3.6V LX Voltage --------------------------------------------------------------------------------------------------- -0.7V to VIN + 0.6V Power Dissipation, PD @ TA = 25°C, SOT23-6-------------------------------------------------------------------------- 0.6W Package Thermal Resistance (Note 2) θ JA -------------------------------------------------------------------------------------------------------------- 170°C/W θ JC -------------------------------------------------------------------------------------------------------------- 130°C/W Junction Temperature Range ------------------------------------------------------------------------------------ -40°C to 150°C Lead Temperature (Soldering, 10 sec.) ----------------------------------------------------------------------------------- 260°C Storage Temperature Range ------------------------------------------------------------------------------------- -65°C to 150°C Dynamic LX voltage in 20ns Duration --------------------------------------------------------------------- IN+3V to GND-5V Recommended Operating Conditions (Note 3) Sil Supply Input Voltage -------------------------------------------------------------------------------------------------- 9V to 36V Junction Temperature Range ------------------------------------------------------------------------------------ -40°C to 125°C AN_SY8291F Rev. 0.9 © 2019 Silergy Corp. Silergy Corp. Confidential- Prepared for Customer Use Only 2 All Rights Reserved. AN_SY8291F Electrical Characteristics (VIN = 12V, VOUT = 5V, L=10μH, COUT =22μF, TA = 25°C, IOUT = 0.5A unless otherwise specified) Parameter Input Voltage Range Input UVLO Threshold Input UVLO Threshold Input UVLO Hysteresis Symbol VIN Test Conditions Min 9 7.5 5.5 Quiescent Current Shutdown Current Feedback Reference Voltage FB Input Current Power FET RON IQ ISHDN VREF IFB RDS(ON)1 IOUT=0, VFB=VREF×105% EN=0 Power FET Current Limit ILIM VFB=VREF×98% EN Rising Threshold EN Falling Threshold Minimum OFF Time Minimum ON Time Soft-start Time Oscillator Frequency Thermal Shutdown Temperature Thermal Shutdown Recovery Hysteresis VENH VENL tOFF tOFF tSS fOSC Rising Falling VUVLO VUVLO_HYS Typ 8 6 2 Max 36 8.5 6.5 立 创 160 0.794 -50 10 0.826 50 µA µA V nA mΩ 2.2 A 180 or 科 VFB=3V 0.81 1.5 rep are dF 1.5 TSD 0.4 100 100 650 300 360 V V ns ns μs kHz 150 °C 50 °C de nti a lP THYS 240 Unit V V V V on fi Note 1: Stresses beyond the “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only. Functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. .C Note 2: θ JA is measured in the natural convection at T A = 25°C on a low effective single layer thermal conductivity test board of JEDEC 51-3 thermal measurement standard. Sil erg yC orp Note 3: The device is not guaranteed to function outside its operating conditions. AN_SY8291F Rev. 0.9 © 2019 Silergy Corp. Silergy Corp. Confidential- Prepared for Customer Use Only 3 All Rights Reserved. AN_SY8291F Typical Performance Characteristics Load Transient Response Efficiency vs Output Current (VIN=12V,VOUT=5V IOUT=0.12~1.2A) 100 95 VOUT 100mV/div 85 80 75 IOUT 70 VIN=12V, VOUT=5V 65 0.01 0.1 1A/div or 科 VIN=19V, VOUT=5V 60 0.001 立 创 Efficiency (%) 90 1 Time (200μs/div) Output Current (A) Shutdown from VIN dF Startup from VIN 10V/div VOUT 5V/div 5V/div IL 1A/div de nti a VLX lP VIN rep are (VIN=12V, VOUT=5V, IOUT=0A) Startup from VIN on fi Time (4ms/div) VOUT 5V/div 5V/div IL 1A/div VIN 10V/div VOUT 5V/div VLX 5V/div IL 1A/div Time (100ms/div) Shutdown from VIN (VIN=12V, VOUT=5V, IOUT=1.2A) VIN 10V/div VOUT 5V/div VLX 5V/div IL 1A/div Sil erg VLX orp 10V/div yC VIN .C (VIN=12V, VOUT=5V, IOUT=1.2A) (VIN=12V, VOUT=5V, IOUT=0A) Time (4ms/div) AN_SY8291F Rev. 0.9 © 2019 Silergy Corp. Time (4ms/div) Silergy Corp. Confidential- Prepared for Customer Use Only 4 All Rights Reserved. AN_SY8291F Startup from Enable Shutdown from Enable (VIN=12V, VOUT=5V, IOUT=0A) (VIN=12V, VOUT=5V, IOUT=0A) 5V/div VEN 5V/div VOUT 5V/div VOUT 5V/div VLX 5V/div IL 1A/div 立 创 VEN Startup from Enable Shutdown from Enable 5V/div IL 1A/div lP 5V/div Time (2ms/div) on fi Short Circuit Protection de nti a VLX dF VOUT VOUT 5V/div IL orp .C (VIN=12V, VOUT=5V IOUT=0A~short) VEN 5V/div VOUT 5V/div VLX 5V/div IL 1A/div Time (2ms/div) Short Circuit Protection (VIN=12V, VOUT=5V IOUT=1.2A~short) VOUT IL 5V/div 1A/div Sil erg yC 1A/div 1A/div (VIN=12V, VOUT=5V, IOUT=1.2A) rep are 5V/div IL Time (100ms/div) (VIN=12V, VOUT=5V, IOUT=1.2A) VEN 5V/div or 科 Time (4ms/div) VLX Time (10ms/div) AN_SY8291F Rev. 0.9 © 2019 Silergy Corp. Time (10ms/div) Silergy Corp. Confidential- Prepared for Customer Use Only 5 All Rights Reserved. AN_SY8291F Output Voltage Ripple Output Voltage Ripple (VIN=12V, VOUT=5V, IOUT=0A) (VIN=12V, VOUT=5V, IOUT=1.2A) VLX IL 50mV/div ΔVOUT 100mV/div VLX 5V/div 5V/div 立 创 ΔVOUT 500mA/div IL Time (4μs/div) Sil erg yC orp .C on fi de nti a lP rep are dF or 科 Time (1μs/div) 1A/div AN_SY8291F Rev. 0.9 © 2019 Silergy Corp. Silergy Corp. Confidential- Prepared for Customer Use Only 6 All Rights Reserved. AN_SY8291F The output capacitor is selected to handle the output ripple noise requirements. Both steady state ripple and transient requirements must be taken into consideration when selecting this capacitor. For the best performance, it is recommended to use an X5R or better grade ceramic capacitor with greater than 22μF capacitance. Operation The SY8291F is an asynchronous Buck regulator that integrates the PWM control, a main switch on the same die. With ultra low RDS(ON) power switch and proprietary PWM control, this regulator can achieve high efficiency and fast transient response. High switch frequency minimizes the external inductor and capacitor size, thus minimizes the PCB area and the cost. The SY8291F also features cycle by cycle current limit, output short circuit protection and thermal shutdown protection. 立 创 Output Inductor L: There are several considerations in choosing this inductor. or 科 1) Choose the inductance to provide the desired ripple current. It is suggested to choose the ripple current to be about 40% of the maximum output current. The inductance is calculated as: V (1  VOUT /VIN, MAX ) L  OUT fSW  IOUT, MAX  40% Applications Information rep are dF Because of the high integration in the SY8291F, the application circuit based on this regulator is rather simple. Only the input capacitor CIN, the output capacitor COUT, the output inductor L, the rectifier diode D and the feedback resistors (R1 and R2) need to be selected for the targeted applications. Where fSW is the switching frequency and IOUT, MAX is the maximum load current. The SY8291F is quite tolerant of different ripple current amplitude. Consequently, the final choice of inductance can be slightly off the calculation value without significantly impacting the performance. 0.81VFB R2 erg Input Capacitor CIN: The ripple current through the input capacitor is calculated as： ICIN_RMS =IOUT  D(1-D) Sil ISAT, MIN  IOUT, MAX  3) yC GND 2) The saturation current rating of the inductor must be selected to be greater than the peak inductor current under full load conditions. VOUT(1-VOUT/VIN,MAX) 2  fSW  L R1 .C 0.81V R1 VOUT -0.81V orp R2 = on fi de nti a lP Feedback Resistor Dividers R1 and R2: Choose R1 and R2 to program the proper output voltage. To minimize the power consumption under light loads, it is desirable to choose large resistance values for both R1 and R2. A value of between 10kΩ and 1MΩ is highly recommended for both resistors. If VOUT is 5V, R1=105kΩ is chosen, then using the following equation, R2 can be calculated to be 20kΩ: VOUT To minimize the potential noise problem, a typical X5R or better grade ceramic capacitor should be placed really close to the IN pin and the negative end of the rectifier. A low ESR ceramic capacitor is recommended with greater than 2.2μF capacitance. The DCR of the inductor and the core loss at the switching frequency must be low enough to achieve the desired efficiency requirement. It is desirable to choose an inductor with DCR